NetBSD: Remove vm_size_t

As noted, this has been deprecated a long time and is no longer present
on x86_64. Remove the typedef.

(backport <#4782>)
(cherry picked from commit 11d36ae)

Author: tgross35

libc-test/semver/netbsd.txt

@@ -1647,6 +1647,5 @@ utmpxname
 utpname
 utrace
 uucred
-vm_size_t
 wait4
 waitid

src/unix/bsd/netbsdlike/netbsd/mod.rs

@@ -13,7 +13,6 @@ pub type fsfilcnt_t = u64;
 pub type idtype_t = c_int;
 pub type mqd_t = c_int;
 type __pthread_spin_t = __cpu_simple_lock_nv_t;
-pub type vm_size_t = crate::uintptr_t; // FIXME(deprecated): deprecated since long time
 pub type lwpid_t = c_uint;
 pub type shmatt_t = c_uint;
 pub type cpuid_t = c_ulong;